Method for responding to failure of specific PDN

ABSTRACT

One embodiment of the present specification provides a method for responding to a failure of a specific packet data network (PDN) in user equipment (UE). The method can comprise the steps of: receiving information on whether a specific PDN has a failure; determining whether the specific PDN is in a failure state on the basis of the received information; and if it is determined that the specific PDN is in the failure state, performing a detach procedure for the specific PDN or a disconnection procedure for the specific PDN, and then, performing an attach procedure to another PDN or a PDN connection establishment procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC § 371 National Stage entry of InternationalApplication No. PCT/KR2015/004072, filed on Apr. 23, 2015, and claimspriority to, U.S. Provisional application No. 61/982,886 filed on Apr.23, 2014, all of which are incorporated by reference in their entiretyherein.

BACKGROUND OF THE INVENTION Field of the Invention

The present specification relates to a method for responding to afailure in a specific packet data network (PDN).

Related Art

In 3GPP in which technical standards for mobile communication systemsare established, in order to handle 4th generation communication andseveral related forums and new technologies, research on Long TermEvolution/System Architecture Evolution (LTE/SAE) technology has startedas part of efforts to optimize and improve the performance of 3GPPtechnologies from the end of the year 2004

SAE that has been performed based on 3GPP SA WG2 is research regardingnetwork technology that aims to determine the structure of a network andto support mobility between heterogeneous networks in line with an LTEtask of a 3GPP TSG RAN and is one of recent important standardizationissues of 3GPP. SAE is a task for developing a 3GPP system into a systemthat supports various radio access technologies based on an IP, and thetask has been carried out for the purpose of an optimized packet-basedsystem which minimizes transmission delay with a more improved datatransmission capability.

An Evolved Packet System (EPS) higher level reference model defined in3GPP SA WG2 includes a non-roaming case and roaming cases having variousscenarios, and for details therefor, reference can be made to 3GPPstandard documents TS 23.401 and TS 23.402. A network configuration ofFIG. 1 has been briefly reconfigured from the EPS higher level referencemodel.

FIG. 1 shows the configuration of an evolved mobile communicationnetwork and FIG. 2 shows interfaces between network nodes shown in FIG.1.

An Evolved Packet Core (EPC) may include various elements. FIG. 1illustrates a Serving Gateway (S-GW) 52, a Packet Data Network Gateway(PDN GW) 53, a Mobility Management Entity (MME) 51, a Serving GeneralPacket Radio Service (GPRS) Supporting Node (SGSN), and an enhancedPacket Data Gateway (ePDG) that correspond to some of the variouselements.

The S-GW 52 is an element that operates at a boundary point between aRadio Access Network (RAN) and a core network and has a function ofmaintaining a data path between an eNodeB 22 and the PDN GW 53.Furthermore, if a terminal (or User Equipment (UE) moves in a region inwhich service is provided by the eNodeB 22, the S-GW 52 plays a role ofa local mobility anchor point. That is, for mobility within an E-UTRAN(i.e., a Universal Mobile Telecommunications System (Evolved-UMTS)Terrestrial Radio Access Network defined after 3GPP release-8), packetscan be routed through the S-GW 52. Furthermore, the S-GW 52 may play arole of an anchor point for mobility with another 3GPP network (i.e., aRAN defined prior to 3GPP release-8, for example, a UTRAN or GlobalSystem for Mobile communication (GSM) (GERAN)/Enhanced Data rates forGlobal Evolution (EDGE) Radio Access Network).

The PDN GW (or P-GW) 53 corresponds to the termination point of a datainterface toward a packet data network. The PDN GW 53 can support policyenforcement features, packet filtering, charging support, etc.Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor pointfor mobility management with a 3GPP network and a non-3GPP network(e.g., an unreliable network, such as an Interworking Wireless LocalArea Network (I-WLAN), a Code Division Multiple Access (CDMA) network,or a reliable network, such as WiMax).

In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53have been illustrated as being separate gateways, but the two gatewaysmay be implemented in accordance with a single gateway configurationoption.

The MME 51 is an element for performing the access of a terminal to anetwork connection and signaling and control functions for supportingthe allocation, tracking, paging, roaming, handover, etc. of networkresources. The MME 51 controls control plane functions related tosubscribers and session management. The MME 51 manages numerous eNodeBs22 and performs conventional signaling for selecting a gateway forhandover to another 2G/3G networks. Furthermore, the MME 51 performsfunctions, such as security procedures, terminal-to-network sessionhandling, and idle terminal location management.

The SGSN handles all packet data, such as a user's mobility managementand authentication for different access 3GPP networks (e.g., a GPRSnetwork and an UTRAN/GERAN).

The ePDG plays a role of a security node for an unreliable non-3GPPnetwork (e.g., an I-WLAN and a Wi-Fi hotspot).

As described with reference to FIG. 1, a terminal (or UE) having an IPcapability can access an IP service network (e.g., IMS), provided by aservice provider (i.e., an operator), via various elements within an EPCbased on non-3GPP access as well as based on 3GPP access.

Furthermore, FIG. 1 shows various reference points (e.g., S1-U andS1-MME). In a 3GPP system, a conceptual link that connects two functionsthat are present in the different function entities of an E-UTRAN and anEPC is called a reference point. Table 1 below defines reference pointsshown in FIG. 1. In addition to the reference points shown in theexample of Table 1, various reference points may be present depending ona network configuration.

TABLE 1 REFERENCE POINT DESCRIPTION S1-MME A reference point for acontrol plane protocol between the E-UTRAN and the MME S1-U A referencepoint between the E-UTRAN and the S-GW for path switching betweeneNodeBs during handover and user plane tunneling per bearer S3 Areference point between the MME and the SGSN that provides the exchangeof pieces of user and bearer information for mobility between 3GPPaccess networks in idle and/or activation state. This reference pointcan be used intra-PLMN or inter-PLMN (e.g. in the case of Inter-PLMNHO). S4 A reference point between the SGW and the SGSN that providesrelated control and mobility support between the 3GPP anchor functionsof a GPRS core and the S-GW. Furthermore, if a direct tunnel is notestablished, the reference point provides user plane tunneling. S5 Areference point that provides user plane tunneling and tunnel managementbetween the S-GW and the PDN GW. The reference point is used for S-GWrelocation due to UE mobility and if the S-GW needs to connect to a non-collocated PDN GW for required PDN connectivity S11 A reference pointbetween the MME and the S-GW SGi A reference point between the PDN GWand the PDN. The PDN may be a public or private PDN external to anoperator or may be an intra-operator PDN, e.g., for the providing of IMSservices. This reference point corresponds to Gi for 3GPP access.

FIG. 3 is an exemplary diagram showing the architecture of a commonE-UTRAN and a common EPC.

As shown in FIG. 3, the eNodeB 20 can perform functions, such as routingto a gateway while RRC connection is activated, the scheduling andtransmission of a paging message, the scheduling and transmission of abroadcast channel (BCH), the dynamic allocation of resources to UE inuplink and downlink, a configuration and providing for the measurementof the eNodeB 20, control of a radio bearer, radio admission control,and connection mobility control. The EPC can perform functions, such asthe generation of paging, the management of an LTE_IDLE state, theciphering of a user plane, control of an EPS bearer, the ciphering ofNAS signaling, and integrity protection.

FIG. 4a is an exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB, and FIG.4b is another exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB.

The radio interface protocol is based on a 3GPP radio access networkstandard. The radio interface protocol includes a physical layer, a datalink layer, and a network layer horizontally, and it is divided into auser plane for the transmission of information and a control plane forthe transfer of a control signal (or signaling).

The protocol layers may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on three lower layers of theOpen System Interconnection (OSI) reference model that is widely knownin communication systems.

The layers of the radio protocol of the control plane shown in FIG. 4aand the radio protocol in the user plane of FIG. 4b are described below.

The physical layer PHY, that is, the first layer, provides informationtransfer service using physical channels. The PHY layer is connected toa Medium Access Control (MAC) layer placed in a higher layer through atransport channel, and data is transferred between the MAC layer and thePHY layer through the transport channel. Furthermore, data istransferred between different PHY layers, that is, PHY layers on thesender side and the receiver side, through the PHY layer.

A physical channel is made up of multiple subframes on a time axis andmultiple subcarriers on a frequency axis. Here, one subframe is made upof a plurality of symbols and a plurality of subcarriers on the timeaxis. One subframe is made up of a plurality of resource blocks, and oneresource block is made up of a plurality of symbols and a plurality ofsubcarriers. A Transmission Time Interval (TTI), that is, a unit timeduring which data is transmitted, is 1 ms corresponding to one subframe.

In accordance with 3GPP LTE, physical channels that are present in thephysical layer of the sender side and the receiver side can be dividedinto a Physical Downlink Shared Channel (PDSCH) and a Physical UplinkShared Channel (PUSCH), that is, data channels, and a Physical DownlinkControl Channel (PDCCH), a Physical Control Format Indicator Channel(PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH), and aPhysical Uplink Control Channel (PUCCH), that is, control channels.

A PCFICH that is transmitted in the first OFDM symbol of a subframecarries a Control Format Indicator (CFI) regarding the number of OFDMsymbols (i.e., the size of a control region) used to send controlchannels within the subframe. A wireless device first receives a CFI ona PCFICH and then monitors PDCCHs.

Unlike a PDCCH, a PCFICH is transmitted through the fixed PCFICHresources of a subframe without using blind decoding.

A PHICH carries positive-acknowledgement (ACK)/negative-acknowledgement(NACK) signals for an uplink (UL) Hybrid Automatic Repeat reQuest(HARQ). ACK/NACK signals for UL data on a PUSCH that is transmitted by awireless device are transmitted on a PHICH.

A Physical Broadcast Channel (PBCH) is transmitted in four former OFDMsymbols of the second slot of the first subframe of a radio frame. ThePBCH carries system information that is essential for a wireless deviceto communicate with an eNodeB, and system information transmittedthrough a PBCH is called a Master Information Block (MIB). In contrast,system information transmitted on a PDSCH indicated by a PDCCH is calleda System Information Block (SIB).

A PDCCH can carry the resource allocation and transport format of adownlink-shared channel (DL-SCH), information about the resourceallocation of an uplink shared channel (UL-SCH), paging information fora PCH, system information for a DL-SCH, the resource allocation of anupper layer control message transmitted on a PDSCH, such as a randomaccess response, a set of transmit power control commands for pieces ofUE within a specific UE group, and the activation of a Voice overInternet Protocol (VoIP). A plurality of PDCCHs can be transmittedwithin the control region, and UE can monitor a plurality of PDCCHs. APDCCH is transmitted on one Control Channel Element (CCE) or anaggregation of multiple contiguous CCEs. A CCE is a logical allocationunit used to provide a PDCCH with a coding rate according to the stateof a radio channel A CCE corresponds to a plurality of resource elementgroups. The format of a PDCCH and the number of bits of a possible PDCCHare determined by a relationship between the number of CCEs and a codingrate provided by CCEs.

Control information transmitted through a PDCCH is called DownlinkControl Information (DCI). DCI can include the resource allocation of aPDSCH (also called a downlink (DL) grant)), the resource allocation of aPUSCH (also called an uplink (UL) grant), a set of transmit powercontrol commands for pieces of UE within a specific UE group, and/or theactivation of a Voice over Internet Protocol (VoIP).

Several layers are present in the second layer. First, a Medium AccessControl (MAC) layer functions to map various logical channels to varioustransport channels and also plays a role of logical channel multiplexingfor mapping multiple logical channels to one transport channel. The MAClayer is connected to a Radio Link Control (RLC) layer, that is, ahigher layer, through a logical channel. The logical channel isbasically divided into a control channel through which information ofthe control plane is transmitted and a traffic channel through whichinformation of the user plane is transmitted depending on the type oftransmitted information.

The RLC layer of the second layer functions to control a data size thatis suitable for sending, by a lower layer, data received from a higherlayer in a radio section by segmenting and concatenating the data.Furthermore, in order to guarantee various types of QoS required byradio bearers, the RLC layer provides three types of operation modes: aTransparent Mode (TM), an Un-acknowledged Mode (UM), and an AcknowledgedMode (AM). In particular, AM RLC performs a retransmission functionthrough an Automatic Repeat and Request (ARQ) function for reliable datatransmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layerperforms a header compression function for reducing the size of an IPpacket header containing control information that is relatively large insize and unnecessary in order to efficiently send an IP packet, such asIPv4 or IPv6, in a radio section having a small bandwidth when sendingthe IP packet. Accordingly, transmission efficiency of the radio sectioncan be increased because only essential information is transmitted inthe header part of data. Furthermore, in an LTE system, the PDCP layeralso performs a security function. The security function includesciphering for preventing the interception of data by a third party andintegrity protection for preventing the manipulation of data by a thirdparty.

A Radio Resource Control (RRC) layer at the highest place of the thirdlayer is defined only in the control plane and is responsible forcontrol of logical channels, transport channels, and physical channelsin relation to the configuration, re-configuration, and release of RadioBearers (RBs). Here, the RB means service provided by the second layerin order to transfer data between UE and an E-UTRAN.

If an RRC connection is present between the RRC layer of UE and the RRClayer of a wireless network, the UE is in an RRC_CONNECTED state. Ifnot, the UE is in an RRC_IDLE state.

An RRC state and an RRC connection method of UE are described below. TheRRC state means whether or not the RRC layer of UE has been logicallyconnected to the RRC layer of an E-UTRAN. If the RRC layer of UE islogically connected to the RRC layer of an E-UTRAN, it is called theRRC_CONNECTED state. If the RRC layer of UE is not logically connectedto the RRC layer of an E-UTRAN, it is called the RRC_IDLE state. SinceUE in the RRC_CONNECTED state has an RRC connection, an E-UTRAN cancheck the existence of the UE in a cell unit, and thus control the UEeffectively. In contrast, if UE is in the RRC_IDLE state, an E-UTRANcannot check the existence of the UE, and a core network is managed in aTracking Area (TA) unit, that is, an area unit greater than a cell. Thatis, only the existence of UE in the RRC_IDLE state is checked in an areaunit greater than a cell. In such a case, the UE needs to shift to theRRC_CONNECTED state in order to be provided with common mobilecommunication service, such as voice or data. Each TA is classifiedthrough Tracking Area Identity (TAI). UE can configure TAI throughTracking Area Code (TAC), that is, information broadcasted by a cell.

When a user first turns on the power of UE, the UE first searches for aproper cell, establishes an RRC connection in the corresponding cell,and registers information about the UE with a core network. Thereafter,the UE stays in the RRC_IDLE state. The UE in the RRC_IDLE state(re)selects a cell if necessary and checks system information or paginginformation. This process is called camp on. When the UE in the RRC_IDLEstate needs to establish an RRC connection, the UE establishes an RRCconnection with the RRC layer of an E-UTRAN through an RRC connectionprocedure and shifts to the RRC_CONNECTED state. A case where the UE inthe RRC_IDLE state needs to establish with an RRC connection includesmultiple cases. The multiple cases may include, for example, a casewhere UL data needs to be transmitted for a reason, such as a callattempt made by a user and a case where a response message needs to betransmitted in response to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

The NAS layer shown in FIG. 3 is described in detail below.

Evolved Session Management (ESM) belonging to the NAS layer performsfunctions, such as the management of default bearers and the managementof dedicated bearers, and ESM is responsible for control that isnecessary for UE to use PS service from a network. Default bearerresources are characterized in that they are allocated by a network whenUE first accesses a specific Packet Data Network (PDN) or accesses anetwork. Here, the network allocates an IP address available for UE sothat the UE can use data service and the QoS of a default bearer. LTEsupports two types of bearers: a bearer having Guaranteed Bit Rate (GBR)QoS characteristic that guarantees a specific bandwidth for thetransmission and reception of data and a non-GBR bearer having the besteffort QoS characteristic without guaranteeing a bandwidth. A defaultbearer is assigned a non-GBR bearer, and a dedicated bearer may beassigned a bearer having a GBR or non-GBR QoS characteristic.

In a network, a bearer assigned to UE is called an Evolved PacketService (EPS) bearer. When assigning an EPS bearer, a network assignsone ID. This is called an EPS bearer ID. One EPS bearer has QoScharacteristics of a Maximum Bit Rate (MBR) and a Guaranteed Bit Rate(GBR) or an Aggregated Maximum Bit Rate (AMBR).

FIG. 5a is a flowchart illustrating a random access process in 3GPP LTE.

The random access process is used for UE 10 to obtain UL synchronizationwith a base station, that is, an eNodeB 20, or to be assigned UL radioresources.

The UE 10 receives a root index and a physical random access channel(PRACH) configuration index from the eNodeB 20. 64 candidate randomaccess preambles defined by a Zadoff-Chu (ZC) sequence are present ineach cell. The root index is a logical index that is used for the UE togenerate the 64 candidate random access preambles.

The transmission of a random access preamble is limited to specific timeand frequency resources in each cell. The PRACH configuration indexindicates a specific subframe on which a random access preamble can betransmitted and a preamble format.

The UE 10 sends a randomly selected random access preamble to the eNodeB20. Here, the UE 10 selects one of the 64 candidate random accesspreambles. Furthermore, the UE selects a subframe corresponding to thePRACH configuration index. The UE 10 sends the selected random accesspreamble in the selected subframe.

The eNodeB 20 that has received the random access preamble sends aRandom Access Response (RAR) to the UE 10. The random access response isdetected in two steps. First, the UE 10 detects a PDCCH masked with arandom access-RNTI (RA-RNTI). The UE 10 receives a random accessresponse within a Medium Access Control (MAC) Protocol Data Unit (PDU)on a PDSCH that is indicated by the detected PDCCH.

FIG. 5b illustrates a connection process in a radio resource control(RRC) layer.

FIG. 5b shows an RRC state depending on whether there is an RRCconnection. The RRC state denotes whether the entity of the RRC layer ofUE 10 is in logical connection with the entity of the RRC layer ofeNodeB 20, and if yes, it is referred to as RRC connected state, and ifno as RRC idle state.

In the connected state, UE 10 has an RRC connection, and thus, theE-UTRAN may grasp the presence of the UE on a cell basis and may thuseffectively control UE 10. In contrast, UE 10 in the idle state cannotgrasp eNodeB 20 and is managed by a core network on the basis of atracking area that is larger than a cell. The tracking area is a set ofcells. That is, UE 10 in the idle state is grasped for its presence onlyon a larger area basis, and the UE should switch to the connected stateto receive a typical mobile communication service such as voice or dataservice.

When the user turns on UE 10, UE 10 searches for a proper cell and staysin idle state in the cell. UE 10, when required, establishes an RRCconnection with the RRC layer of eNodeB 20 through an RRC connectionprocedure and transits to the RRC connected state.

There are a number of situations where the UE staying in the idle stateneeds to establish an RRC connection, for example, when the userattempts to call or when uplink data transmission is needed, or whentransmitting a message responsive to reception of a paging message fromthe EUTRAN.

In order for the idle UE 10 to be RRC connected with eNodeB 20, UE 10needs to perform the RRC connection procedure as described above. TheRRC connection procedure generally comes with the process in which UE 10transmits an RRC connection request message to eNodeB 20, the process inwhich eNodeB 20 transmits an RRC connection setup message to UE 10, andthe process in which UE 10 transmits an RRC connection setup completemessage to eNodeB 20. The processes are described in further detail withreference to FIG. 6.

1) The idle UE 10, when attempting to establish an RRC connection, e.g.,for attempting to call or transmit data or responding to paging fromeNodeB 20, sends an RRC connection request message to eNodeB 20.

2) When receiving the RRC connection message from UE 10, eNodeB 20accepts the RRC connection request from UE 10 if there are enough radioresources, and eNodeB 20 sends a response message, RRC connection setupmessage, to UE 10.

3) When receiving the RRC connection setup message, UE 10 transmits anRRC connection setup complete message to eNodeB 20. If UE 10successfully transmits the RRC connection setup message, UE 10 happensto establish an RRC connection with eNodeB 20 and switches to the RRCconnected state.

FIG. 6 illustrates connection between an EPC and an IP MultimediaSubsystem (IMS).

The IMS is a network technique that enables not only a wired terminalbut also a wireless terminal to perform IP-based packet switching (PS)and is proposed to connect both wired/wireless terminals through the IP(All-IP).

An IMS-based network includes control signaling, registration, and aCall Session Control Function (CSCF) for processing a session procedure.The CSCF may include a Proxy-CSCF (P-CSCF), a Serving-CSCF (S-CSCF), andan Interrogating-CSCF (I-CSCF). The P-CSCF operates as a first accesspoint for a UE in the IMS-based network. The S-CSCF processes a sessionin the IMS network. That is, the S-SCSF is an entity serving to route asignal and routes a session in the IMS network. The I-CSCF operates asan access point to another entity in the IMS network.

Under the IMS, an IP-based session is controlled by a session initiationprotocol (SIP). The SIP is a protocol for controlling a session, whichis a signaling protocol that specifies a procedure in which terminals tocommunicate identify each other to detect locations thereof and generatea multimedia service session therebetween or delete or change agenerated session. The SIP uses an SIP Uniform Resource Identifier(URI), similar to an email address, to distinguish each user, thusproviding a service without being subjected to an IP address.

Referring to FIG. 6, a first P-GW 53 a of the EPC is connected to theP-CSCF 61 of the IMS, and the P-CSCF 61 is connected to the S-CSCF 62.

Further, a second P-GW 53 b of the EPC is connected to a network of anInternet service provider.

When a network failure occurs to disconnect the first P-GW 53 a from theP-CSCF 61, all IMS-based services are stopped. Here, the IMS-basedservices include a very important service, for example, a Voice over LTE(VoLTE). When the VoLTE service is stopped, a user suffers seriousinconvenience.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to present a methodthat can solve the aforementioned problem.

To achieve the foregoing object, one embodiment of the presentspecification provides a method for a user equipment (UE) to respond toa failure in a specific packet data network (PDN). The method mayinclude: receiving information on whether a specific PDN has a failure;determining whether the specific PDN is in a failure state on the basisof the received information; and if it is determined that the specificPDN is in the failure state, performing a detach procedure with respectto the specific PDN or a disconnection procedure for the specific PDNand performing an attach procedure or a PDN connection establishmentprocedure with respect to another PDN.

When the attach procedure or PDN connection establishment procedure withrespect to the other PDN is performed, the method may includetransmitting a request message comprises a PDN type having no failure.

The information on whether the specific PDN has the failure may beimplicitly or explicitly received.

When an indication explicitly indicating the information on whether thespecific PDN has the failure is received, the method may further includedetermining whether a normal service is available on the other PDN.

The information on whether the specific PDN has the failure may bereceived by User Equipment (UE), Mobility Management Entity (MME), PDN,or Evolved Packet System (EPS) bearer.

To achieve the foregoing object, one embodiment of the presentspecification provides a method for an entity responsible for a controlplane to respond to a failure in a specific packet data network (PDN).The method may include: receiving information on whether a specific PDNhas a failure; determining whether the specific PDN is in a failurestate on the basis of the received information; and if it is determinedthat the specific PDN is in the failure state, performing, for a userequipment (UE), an attach procedure or a PDN connection establishmentprocedure with respect to another PDN.

When the attach procedure or PDN connection establishment procedure withrespect to the other PDN is performed, the method may further includeacquiring subscriber information on the UE from a Home Subscriber Server(HSS) although having at least one of the subscriber information on theUE and context of the UE.

The information on whether the specific PDN has the failure may beimplicitly or explicitly received.

When an indication explicitly indicating the information on whether thespecific PDN has the failure is received, the method may further includedetermining whether a normal service is available on the other PDN.

The information on whether the specific PDN has the failure may bereceived by UE, MME, PDN, or EPS bearer.

To achieve the foregoing object, one embodiment of the presentspecification provides a method for a gateway to respond to a failure ina specific PDN. The method may include: receiving information on whethera specific PDN has a failure; determining whether the specific PDN is ina failure state on the basis of the received information; and if it isdetermined that the specific PDN is in the failure state, selectinganother PDN during an attach procedure or a PDN connection establishmentprocedure.

According to the embodiments of the present invention, the problems inthe related art can be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an evolved mobile communicationnetwork.

FIG. 2 shows interfaces between network nodes shown in FIG. 1

FIG. 3 is an exemplary diagram showing the architecture of a commonE-UTRAN and a common EPC.

FIG. 4a is an exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB.

FIG. 4b is another exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB.

FIG. 5a is a flowchart illustrating a random access process in 3GPP LTE.

FIG. 5b illustrates a connection process in a radio resource control(RRC) layer.

FIG. 6 illustrates connection between an EPC and an IP MultimediaSubsystem (IMS).

FIG. 7 illustrates an example of restoring a path, disconnected by anetwork failure, through a bypass.

FIG. 8 is a flowchart illustrating an improved operation of a HomeSubscriber Server (HSS) according to one embodiment of the presentspecification.

FIG. 9 is a flowchart illustrating an improved operation of a UEaccording to one embodiment of the present specification.

FIG. 10 is a flowchart illustrating an improved operation of an MMEaccording to one embodiment of the present specification.

FIG. 11 is a flowchart illustrating an improved operation of a P-GWaccording to one embodiment of the present specification.

FIG. 12 is a block diagram illustrating a configuration of a UE 100, anMME 510, a P-GW 530, and an HSS 540 according to one embodiment of thepresent invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention is described in light of UMTS (Universal MobileTelecommunication System) and EPC (Evolved Packet Core), but not limitedto such communication systems, and may be rather applicable to allcommunication systems and methods to which the technical spirit of thepresent invention may apply.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes themeaning of the plural number unless the meaning of the singular numberis definitely different from that of the plural number in the context.In the following description, the term ‘include’ or ‘have’ may representthe existence of a feature, a number, a step, an operation, a component,a part or the combination thereof described in the specification, andmay not exclude the existence or addition of another feature, anothernumber, another step, another operation, another component, another partor the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

In the drawings, user equipments (UEs) are shown for example. The UE mayalso be denoted a terminal or mobile equipment (ME). The UE may be alaptop computer, a mobile phone, a PDA, a smartphone, a multimediadevice, or other portable device, or may be a stationary device such asa PC or a car mounted device.

Definition of Terms

For a better understanding, the terms used herein are briefly definedbefore going to the detailed description of the invention with referenceto the accompanying drawings.

A GERAN is an abbreviation of a GSM EDGE Radio Access Network, and itrefers to a radio access section that connects a core network and UE byGSM/EDGE.

A UTRAN is an abbreviation of a Universal Terrestrial Radio AccessNetwork, and it refers to a radio access section that connects the corenetwork of the 3rd generation mobile communication and UE.

An E-UTRAN is an abbreviation of an Evolved Universal Terrestrial RadioAccess Network, and it refers to a radio access section that connectsthe core network of the 4th generation mobile communication, that is,LTE, and UE.

An UMTS is an abbreviation of a Universal Mobile TelecommunicationSystem, and it refers to the core network of the 3rd generation mobilecommunication.

UE or an MS is an abbreviation of User Equipment or a Mobile Station,and it refers to a terminal device.

An EPS is an abbreviation of an Evolved Packet System, and it refers toa core network supporting a Long Term Evolution (LTE) network and to anetwork evolved from an UMTS.

A PDN is an abbreviation of a Public Data Network, and it refers to anindependent network where a service for providing service is placed.

A PDN connection refers to a connection from UE to a PDN, that is, anassociation (or connection) between UE represented by an IP address anda PDN represented by an APN.

A PDN-GW is an abbreviation of a Packet Data Network Gateway, and itrefers to a network node of an EPS network which performs functions,such as the allocation of a UE IP address, packet screening & filtering,and the collection of charging data.

A Serving gateway (Serving GW) is a network node of an EPS network whichperforms functions, such as mobility anchor, packet routing, idle modepacket buffering, and triggering an MME to page UE.

A Policy and Charging Rule Function (PCRF) is a node of an EPS networkwhich performs different QoS for each service flow and a policy decisionfor dynamically applying a charging policy.

An Access Point Name (APN) is the name of an access point that ismanaged in a network and provides to UE. That is, an APN is a characterstring that denotes or identifies a PDN. Requested service or a network(PDN) is accessed via a P-GW. An APN is a name (character string, e.g.,‘internet.mnc012.mcc345.gprs’) previously defined within a network sothat the P-GW can be searched for.

A Tunnel Endpoint Identifier (TEID) is an end point ID of a tunnel setup between nodes within a network and is set in each section as a bearerunit of each terminal.

A NodeB is an eNodeB of a UMTS network and installed outdoors. The cellcoverage of the NodeB corresponds to a macro cell.

An eNodeB is an eNodeB of an Evolved Packet System (EPS) and isinstalled outdoors. The cell coverage of the eNodeB corresponds to amacro cell.

An (e)NodeB is a term that denotes a NodeB and an eNodeB.

An MME is an abbreviation of a Mobility Management Entity, and itfunctions to control each entity within an EPS in order to provide asession and mobility for UE.

A session is a passage for data transmission, and a unit thereof may bea PDN, a bearer, or an IP flow unit. The units may be classified into aunit of the entire target network (i.e., an APN or PDN unit) as definedin 3GPP, a unit (i.e., a bearer unit) classified based on QoS within theentire target network, and a destination IP address unit.

A PDN connection is a connection from UE to a PDN, that is, anassociation (or connection) between UE represented by an IP address anda PDN represented by an APN. It means a connection between entities(i.e., UE-PDN GW) within a core network so that a session can be formed.

UE context is information about the situation of UE which is used tomanage the UE in a network, that is, situation information including anUE ID, mobility (e.g., a current location), and the attributes of asession (e.g., QoS and priority)

A Non-Access-Stratum (NAS) is a higher stratum of a control planebetween UE and an MME. The NAS supports mobility management and sessionmanagement between UE and a network, IP address maintenance, and so on.

RAT is an abbreviation of Radio Access Technology, and it means a GERAN,a UTRAN, or an E-UTRAN.

ANDSF (Access Network Discovery and Selection Function): As one networkentity, a policy is provided to discover and select access which theterminal can use by the unit of the provider

Meanwhile, a description is made hereinafter with reference to drawings.

FIG. 7 illustrates an example of restoring a path, disconnected by anetwork failure, through a bypass.

0) First, a UE 100 initiates an Internet Protocol-Connectivity AccessNetwork (IP-CAN) session. To this end, the UE 100 may transmit a PDNConnectivity Request message.

1) An MME 510 performs a P-CSCF discovery procedure. The P-CSCFdiscovery procedure is for requesting a list of P-CSCF addresses. Tothis end, for example, the MME 510 may transmit a Create Session Requestmessage or Create PDP Context Request message to a P-GW 530 or SGSN viaan S-GW.

2) The P-GW 530 receives a result of the P-CSCF discovery procedure.That is, the P-GW 530 receives a list of P-CSCF addresses. The list ofP-CSCF addresses may be received through a Create Session Responsemessage or Create PDP Context Response message.

3) The P-GW 530 transmits a Diameter Credit Control Request (CCR) to aPCRF 550 in order to request Policy and Charging Control (PCC) rules.

4) The PCRF 550 transmits a Diameter Credit Control Answer (CCA)including PCC rules to the P-GW 530.

5) The UE 100 transmits a registration request message, for example, anSIP Register message, to a P-CSCF 610 based on the received list ofP-CSCF addresses.

6) The P-CSCF 610 transmits, to the PCRF 550, an Rx Push messageincluding an address thereof in order to report that the P-CSCF 610 isselected by the UE.

7) The PCRF 550 transmits an Rx Push Response message in response.

8) The PCRF 550 transmits a Gx Push message to the P-GW 530 in order toreport the address of the P-CSCF 610.

9) The P-GW 530 transmits a Gx Push Response message in response.

In addition, the P-GW 530 stores the address of the P-CSCF 610 for theUE. The P-GW 530 monitors the state of the P-CSCF 610.

10) The P-CSCF 610 transmits a response message to the registrationmessage, for example, a 200 OK message, to the UE 100.

11) Meanwhile, when the P-GW 530 detects that there is a problem orfailure in connection to the P-CSCF 610 as a result of monitoring thestate of the P-CSCF 610, the P-GW 530 transmits a new list excluding theaddress of the P-CSCF 610 having a failure (that is, a new listincluding addresses of other P-CSCFs) to all UEs that have establishedconnection to the P-CSCF 610 having a failure. To this end, the P-GW 530transmits an Update PDP Context Request message or Update Bearer Requestmessage to the MME 510.

12) When the UE 100 transmits a response to the reception of the newlist, the MME 510 transmits an Update PDP Context Response message orUpdate Bearer Response message to the P-GW 530.

13) Meanwhile, the UE 100 discovers a new P-CSCF through the new listand transmits a registration request message to the new P-CSCF.

As described above, when the P-GW 530 detects that there is a failure inconnection to the P-CSCF 610, the P-GW 530 transmits a new listexcluding the address of the P-CSCF 610 having a failure to the UE,thereby quickly restoring a failure.

However, although the P-GW 530 sends a new list, a failure may notquickly be restored depending on a situation.

For example, in addition to a physical failure, when a routing table ofP-CSCF addresses in the entire corresponding PDN is damaged, otherP-CSCF addresses that the P-GW 530 already has may also be useless.Thus, a registration request message, which the UE 100 transmits toanother P-CSCF on a new list provided from the P-GW 530, may not arriveat the other P-CSCF.

For another example, when a failure occurs in the entire PDN, there isno available P-CSCF on the currently connected PDN.

As a result, even the method illustrated in FIG. 7 may not enablecritical services including a VoLTE service, and thus a user has seriousinconvenience in receiving services.

Moreover, when the UE 100 continuously reattempts transmission/receptionservices, signaling increases in a network to cause unnecessaryconsumption of resources and a very long delay time may be involved fromtime an initial service is attempted even to succeed in receiving aservice.

EMBODIMENTS OF THE PRESENT SPECIFICATION

Therefore, embodiments of the present specification provide a method forquickly recognizing a network failure and actively resuming a service.An effective control method proposed in the present specification may beformed of one or more of the following operations.

I. P-GW Detecting and Evaluating Failure in Specific PDN

The P-GW 530 identifies whether the same service is provided via adifferent PDN. For example, when a failure occurs in an IPv4 PDN, theP-GW 530 identifies whether the same service is provided via an IPv6PDN. When it is possible to connect to the different PDN in order toprovide the service, the P-GW 530 recognizes that a corresponding IPversion of an IP address needs to be allocated to the UE.

The P-GW 530 identifies whether the PDN of the UE is a PDN that providesa specific service (for example, a PDN that provides a VoLTE-relatedservice). Such identification may be performed based on configurationinformation, information received from the PCRF, or P-CSCF informationmanaged for connection setup.

II. P-GW Actively Notifying Another Network Node of NetworkFailure/Inducing Change of Connection Configuration of UE

The P-GW 530 identifies the availability of a network node belonging toa PDN having no failure and updates a list of P-CSCF addressesregardless of preference of a service provider for a PDN type (beforethe service provider recognizes a network failure and changes aconfiguration), thereby preparing for transmission to the UE.

Further, the P-GW 530 may notify the UE or network node through variousroutes that there is a need to change the connection configuration ofthe UE, which may be achieved by one of various operations illustratedbelow.

1) The P-GW 530 may notify the MME via the S-GW that there is a need tochange the connection configuration of the UE, which may be achieved byusing a general GTP protocol or by adding a new field to the general GTPprotocol. Particularly, in a case of an IPv4 failure, the P-GW 530 mayimplicitly/explicitly report that there is a need to establish an IPv6connection (and vice versa).

For another example, the P-GW 530 may store relevant information on aneed to change the connection configuration of the UE in the MME.

In a reattach procedure or PDN reconnection, not only subscriberinformation and requests transmitted from the UE but also informationfor determining a PDN type based on information on a failure situationmay be transmitted to the P-GW (for example, using a Create SessionRequest message). Here, the reattach procedure refers to an attachprocedure performed following a detach procedure. The PDN reconnectionrefers to a PDN connection request procedure performed again following aPDN disconnection.

2) More actively, when a detach or PDN disconnection-related message istransmitted to the UE, the P-GW 530 may implicitly/explicitly transmitinformation indicating that connection to another PDN is needed to theUE.

3) The relevant information may be stored in the UE.

The UE may request a session from a PDN having no failure through areattach/PDN reconnection request message.

4) The P-GW 530 may notify a Home Subscriber Server (HSS) via theS-GW/MME that there is a need to change the connection configuration ofthe UE.

The HSS may temporarily change and adjust the subscriber informationsuch that a PDN type having a failure is not allowed to be included in aPDN type allowed for connection.

5) The P-GW 530 may implicitly/explicitly transmit information on a PDNhaving a failure to a third network node that can obtain an address of anetwork node needed for connection to a specific PDN, such as a P-CSCFincluding a DHCP server. Specifically, when the UE or network node sendsa request message to acquire an address of a network node needed forconnection to a specific PDN, the P-GW 530 may store the relevantinformation to send a network address for connection to a PDN having nofailure and may manage a list of available networks.

6) The P-GW may temporarily adjust the configuration.

In addition to notification to another network node, the P-GW 530changes the configuration of the P-GW (the P-GW dynamically changes theconfiguration via determination, instead of the service providerupdating the configuration), adjusts the configuration such that a PDNtype having a failure is not allowed, and performs an operation neededfor detach/PDN disconnection.

Hereinafter, an operation according to an embodiment of the presentinvention is described in detail with reference to drawings. Thefollowing operation relates to an active failure control mechanismperformed to hand over a service to a network having no failure when aspecific PDN type failure occurs. This operation may allow a user to beprovided with a continued service as quickly as possible when a failureoccurs.

Further, a network node (for example, P-GW) detecting a failure directlyattempts to immediately resume a service for UEs connected to thenetwork node in order to reduce time to resume a service.

FIG. 8 is a flowchart illustrating an improved operation of the HSSaccording to one embodiment of the present specification.

1) A network node (for example, a P-GW, S-GW, MME, DNS server, HSS,PCRF, ePDG, TWAN, AAA server, and the like) detects a failure in aspecific PDN.

A failure may be detected by a combination of one or more of thefollowing methods.

a. A service provider directly transmits a service provider command orupdates a configuration so that all or some network nodes (for example,a P-GW, S-GW, MME, DNS server, HSS, PCRF, ePDG, TWAN, AAA server, andthe like) may recognize the failure in the specific PDN.

b. In a case where a DNS query is attempted to discover a network node(for example, a P-CSCF) of the specific PDN, when the number of attemptfailures, which is calculated for a certain period of time, is greaterthan a specific threshold, the entire PDN is considered to have afailure.

c. In a case where data/signal is transmitted to a network node (forexample, a P-CSCF) of the specific PDN, when no acknowledgement isreceived for a certain period of time or when the number of receivedresponses to transmission failure is greater than a specific threshold,the entire PDN is considered to have a failure.

d. When time to discover an address of a network node of the specificPDN or delay time in data/signal transmission between network nodesrelatively increases to be greater than a specific threshold, the entirePDN is considered to have a failure.

e. When time to discover an address of a network node of the specificPDN or delay time in data/signal transmission between network nodesrelatively increases and the number of times this situation continuouslyoccurs is greater than a specific threshold, the entire PDN isconsidered to have a failure.

The failure in the PDN may refer to a physical failure that occurs inall network nodes or some network nodes belonging to the PDN to disablethe operations of the network nodes and may also refer to a state inwhich an address of a network node belonging to the PDN is not detectedso that data/signal may not be transmitted. Further, although theaddress of the network node is detected or data/signal may betransmitted, time to detect the address of the network node/transmissiondelay time or success rate is not included in a normal service providingrange or when network node address discovery/transmission failure rateexceeds a normal service providing range, the PDN may be considered tohave a failure. The thresholds may be preset by the service provider orbe individually or collectively updated.

2-3) Information on the detected failure may be transmitted to anothernetwork (for example, a P-GW, S-GW, MME, DNS server, HSS, PCRF, ePDG,TWAN, AAA server, and the like).

For example, information on a failure in a specific PDN detected by theP-GW 530 may be transmitted to the MME 510 via the S-GW 520, and the MME510 may forward this information to the HSS 540 via processing or as itis. A basic GTP protocol message or newly defined message may be used totransmit this information.

An information transmission unit may be a UE, a PDN, and an EPS bearer,or information may be transmitted by network node (for example, an MME).

For example, subscriber information may be transmitted by MME betweenthe MME and the HSS to signal the failure in the specific PDN to theHSS. However, if subscriber information is transmitted by UE, thefailure in the specific PDN may be signaled to the HSS only with respectto a UE connected to the PDN currently having a failure.

For example, the information on the failure in the specific PDN, whichis transmitted from the P-GW 530 to the MME 510 via the S-GW 520, may betransmitted by PDN using a GPRS Tunneling Protocol (GTP) tunnel or betransmitted only once by MME to each MME using a new message or acontrol signaling message between network nodes.

4) After recognizing the failure in the specific PDN, the HSS 540updates subscriber information including the information on the PDN.That is, the HSS 540 adjusts the subscriber information such that a PDNtype having a failure is not allowed as a PDN type allowed forconnection. That is, the subscriber information has no permission forthe PDN type, thus preventing an attempt to connect to the PDN.

For example, when a failure occurs in an IPv6 PDN, the HSS 540 changesspecific subscriber information, from indicating that IPv6 and IPv4 PDNsare allowed to indicating only the IPv4 PDN is allowed.

5) After updating the subscriber information, the HSS 540 transmits amessage to the MME 510 to report the change of the subscriberinformation.

Alternatively, when the MME 510 performs a process of acquiringsubscriber information, the updated subscriber information istransmitted to the MME 510. For example, when an attach procedure is inprogress, the MME 510 performs a process of acquiring the subscriberinformation from the HSS 540, in which the changed subscriberinformation may be transmitted to the MME 510.

A process has been described in which when a network node detects afailure in a specific PDN and notifies an HSS of the failure, the HSSupdates subscriber information and transmits the updated subscriberinformation to an MME. However, when it is detected that the failure inthe specific PDN is restored after a certain period of time, a failurerestoration indication is transmitted to the HSS and the HSS updates thesubscriber information and transmits the updated subscriber informationto the MME.

Failure restoration may be detected by a combination of one or more ofthe following methods.

a. A service provider directly transmits a service provider command orupdates a configuration so that all or some network nodes (for example,a P-GW, S-GW, MME, DNS server, HSS, PCRF, ePDG, TWAN, AAA server, andthe like) may recognize the restoration of the failure in the specificPDN.

b. In a case where although not for a service (because an attempt at aservice is not currently made to the PDN having the failure), a DNSquery is periodically transmitted to discover a network node (forexample, a P-CSCF) of the specific PDN internally in the network, whenthe number of successes, which is calculated for a certain period oftime, is greater than a specific threshold, it is considered that theentire PDN is restored from the failure.

c. In a case where, which although not for a service (because an attemptat a service is not currently made to the PDN having the failure), apolling signal is transmitted to a network node (for example, a P-CSCF)of the specific PDN internally in the network and an acknowledgement isnormally received for a certain period of time, when the number ofreceived responses to success, which is calculated for a certain periodof time, is greater than a specific threshold, it is considered that theentire PDN is restored from the failure.

d. Although not for a service (because an attempt at a service is notcurrently made to the PDN having the failure), when time to discover anaddress of a network node of the specific PDN or delay time in pollingsignal transmission between network nodes internally in the network iswithin a specific threshold range, it is considered that the entire PDNis restored from the failure.

e. Although not for a service (because an attempt at a service is notcurrently made to the PDN having the failure), when time to discover anaddress of a network node of the specific PDN or delay time in pollingsignal transmission between network nodes internally in the network iswithin a specific threshold range and the number of times this situationcontinuously occurs is greater than a specific threshold, it isconsidered that the entire PDN is restored from the failure.

FIG. 9 is a flowchart illustrating an improved operation of the UEaccording to one embodiment of the present specification.

1) A network node (for example, a P-GW, S-GW, MME, DNS server, HSS,PCRF, ePDG, TWAN, AAA server, and the like) detects a failure in aspecific PDN. A failure detecting method has been described above.

2-3) Information on the failure in the specific PDN detected in thenetwork is implicitly/explicitly transmitted to the UE 100 and the HSS540. The information on the failure is transmitted as described above.

4) After recognizing the failure in the specific PDN, the HSS 540updates subscriber information including the information on the PDN.

5) The UE 100, which has implicitly/explicitly received the informationon the failure in the specific PDN, determines whether the specific PDNis in a failure state. If the specific PDN is in the failure state, theUE 100 is disconnected from the PDN having the failure and establishesconnection to a PDN enabling a normal service. That is, the UE 100performs a detach operation and then a reattach operation or performsPDN disconnection and then a reestablishment procedure.

Specifically, when the UE 100 explicitly receives the information on thefailure in the PDN, that is, a PDN failure indication, and determinesthat the specific PDN is in the failure state based on the reception,the UE 100 may explicitly determine a PDN type providing a normalservice and may transmit a connection request message to the network ina reattach/PDN reestablishment process.

Alternatively, when the UE 100 implicitly receives the information onthe failure in the specific PDN and determines that the specific PDN isin the failure state based on the reception, the UE 100 transmits anattach request message/PDN connection request message to perform anattach/PDN establishment process. Here, a network receiving the requestmessage, that is, the MME, may establish connection to a PDN typeproviding a normal service based on subscriber information or theinformation on the failure in the specific PDN stored in the MME. Forexample, according to a conventional technique, when the MME already hascontext of a UE, the MME may not perform a process for locationregistration in the HSS/subscriber information acquiring. However, whenthe MME recognizes a failure in a specific PDN, the MME performs aprocess of acquiring subscriber information from the HSS although havingthe context of the UE. Accordingly, the MME performs a subsequentprocedure for connection to a PDN having no failure based on thesubscriber information updated by HSS.

The foregoing embodiment illustrates a process after a UE acquiresinformation on a failure in a specific PDN. If the failure in thespecific PDN is restored after a certain period of time, a similarprocess for acquiring information on the restoration of the failure andestablishing connection to a new PDN may be performed.

FIG. 10 is a flowchart illustrating an improved operation of the MMEaccording to one embodiment of the present specification.

1) A network node (for example, a P-GW, S-GW, MME, DNS server, HSS,PCRF, ePDG, TWAN, AAA server, and the like) detects a failure in aspecific PDN. A failure detecting method has been described above.

2) Information on the failure in the specific PDN detected in thenetwork is implicitly/explicitly transmitted to the MME 510. Theinformation on the failure is transmitted as described above.

3) The MME 510 implicitly/explicitly transmits the information on thefailure in the specific PDN to the HSS 540. The information on thefailure is transmitted as described above.

4) After recognizing the failure in the specific PDN, the HSS 540updates subscriber information including the information on the PDN.

5) The MME 510, which has implicitly/explicitly received the informationon the failure in the specific PDN, determines whether the specific PDNis in a failure state. If the specific PDN is in the failure state, theMME 510 is disconnected from the PDN having the failure and establishesconnection to a PDN enabling a normal service. That is, the MME 510performs a detach operation and then a reattach operation or performsPDN disconnection and then a reestablishment procedure.

Specifically, the MME 510 operates as follows.

a. The MME 510 may receive a request message for setup of connection toa PDN type providing a normal service from the UE 100.

b. The MME 510 may receive, from the HSS 540, subscriber informationindicating that only a PDN type providing a normal service is allowed.

c. The MME 510 acquires and stores/configures information on a failurein a specific PDN type from another network node to select a PDN typeproviding a normal service. This information is transmitted to the P-GW530.

d. After acquiring the information on the failure in the specific PDNtype from the other network node, the MME 510 may transmit, to the UE,an indication for detaching/attaching the UE 100 or PDNdisconnection/reestablishment. Here, the information on the PDN havingthe failure may also be explicitly/implicitly transmitted.

e. After acquiring the information on the failure in the specific PDNtype from the other network node, the MME 510 acquires subscribeinformation from the HSS in order to respond to the connection setuprequest from the UE, although already having UE context.

A process after the MME 510 acquires information on a failure in aspecific PDN has been described. If the failure in the specific PDN isrestored after a certain period of time, a similar process for acquiringinformation on the restoration of the failure and establishingconnection to a new PDN may be performed.

FIG. 11 is a flowchart illustrating an improved operation of the P-GWaccording to one embodiment of the present specification.

1) A network node (for example, a P-GW, S-GW, MME, DNS server, HSS,PCRF, ePDG, TWAN, AAA server, and the like) detects a failure in aspecific PDN. A failure detecting method has been described above.

2) Information on the failure in the specific PDN detected in thenetwork is implicitly/explicitly transmitted to the MME 510. Theinformation on the failure is transmitted as described above.

3) The MME 510 implicitly/explicitly transmits the information on thefailure in the specific PDN to the HSS 540. The information on thefailure is transmitted as described above.

4) After recognizing the failure in the specific PDN, the HSS 540updates subscriber information including the information on the PDN.

5) The MME 510, which has implicitly/explicitly received the informationon the failure in the specific PDN, disconnects the UE 100 from the PDNhaving the failure and establishes connection of the UE 100 to a PDNproviding a normal service. That is, the MME 510 performs a detachoperation and then a reattach operation or performs PDN disconnectionand then a reestablishment procedure.

Here, when the P-GW 530 receives a request message (for example, aconnection setup request message) during the reattach or PDNreestablishment process, a PDN type providing a normal service isselected based on the foregoing stored/configured information.

Additionally, in operation 2), since pieces of information on PDNshaving a failure are implicitly/explicitly transmitted/stored in a thirdnetwork node that can obtain an address of a network node needed forconnection to a specific PDN, such as a P-CSCF, when a request messageis transmitted to acquire an address of a network node needed forconnection to a specific PDN, the P-GW 530 may store the relevantinformation to send a network address for connection to a PDN having nofailure and may manage a list of available networks.

A process after the P-GW or another network node acquires information ona failure in a specific PDN has been described. If the failure in thespecific PDN is restored after a certain period of time, a similarprocess for acquiring information on the restoration of the failure andestablishing connection to a new PDN may be performed.

The aforementioned details may be implemented in hardware, which isdescribed with reference to FIG. 17.

FIG. 12 is a block diagram illustrating a configuration of the UE 100,the MME 510, the P-GW 530, and the HSS 540 according to one embodimentof the present invention.

As illustrated in FIG. 12, the UE 100 includes a storage means 101, acontroller 102, and a transceiver 103. The MME 510 includes a storagemeans 511, a controller 512, and a transceiver 513. The P-GW 530includes a storage means 531, a controller 532, and a transceiver 533.The HSS 540 includes a storage means 541, a controller 542, and atransceiver 543.

The storage means 101, 511, 531, and 541 store the foregoing methods.

The controllers 102, 512, 532, and 542 control the storage means 101,511, 531, and 541 and the transceivers 103, 513, 533, and 543.Specifically, the controllers 102, 512, 532, and 542 perform theforegoing methods stored in the storage means 101, 511, 531, and 541.The controllers 102, 512, 532, and 542 transmit the foregoing signalsthrough the transceivers 103, 513, 533, and 543.

Although exemplary embodiments of the present invention have beenillustrated above, the scope of the present invention is not limited bythese specific embodiments. Therefore, the present invention may bechanged, modified, or adapted variously without departing from the ideaof the present invention and the appended claims.

What is claimed is:
 1. A method for a user equipment (UE) to respond toa failure in a packet data network (PDN), the method comprising:receiving first information from a PDN gateway (P-GW), wherein the firstinformation represents that a first PDN based on an internet protocolversion 6 (IPv6) is in a failure state; receiving second information onthe need to change the PDN; determining, by the UE, that a second PDNbased on an IP version 4 (IPv4) is capable of providing the same serviceas provided by the first PDN and is not in a failure state, based on thesecond information; performing a detach procedure or a disconnectionprocedure with the first PDN; and performing an attach procedure and aPDN connection establishment procedure with the second PDN, wherein thePDN connection establishment procedure includes: inserting PDN typeinformation representing the IPv4 into a PDN connectivity requestmessage; and transmitting the PDN connectivity request message includingthe PDN type information representing the IPv4.
 2. The method of claim1, wherein the first information that the first PDN has failed isimplicitly received.
 3. The method of claim 1, wherein the firstinformation is received by a Mobility Management Entity (MME), thesecond PDN, or an Evolved Packet System (EPS) bearer.
 4. The method ofclaim 1, wherein the first information that the first PDN has failed isexplicitly received.
 5. A method for an entity responsible for a controlplane to respond to a failure in a packet data network (PDN), the methodcomprising: receiving, from a PDN gateway (P-GW), first information,wherein the first information represents that a first PDN based on aninternet protocol version 6 (IPv6) is in a failure state; receiving,from the gateway, second information requesting a PDN change;determining that a second PDN based on an IP version 4 (IPv4) is capableof providing the same service as provided by the first PDN and is not ina failure state, based on the second information; performing, for a userequipment (UE), an attach procedure and a PDN connection establishmentprocedure with a second PDN, wherein the PDN connection establishmentprocedure includes: inserting PDN type information representing the IPv4into a PDN connectivity request message; and transmitting the PDNconnectivity request message including the PDN type informationrepresenting the IPv4.
 6. The method of claim 5, wherein when the attachprocedure or PDN connection establishment procedure with the second PDNis performed, the entity subscriber information on the UE from a HomeSubscriber Server (HSS), even when the entity has at least one of thesubscriber information on the UE and context information of the UE. 7.The method of claim 5, wherein the first information that the first PDNhas failed is implicitly received.
 8. The method of claim 7, furthercomprising: when the first information is explicitly received,determining whether a normal service is available on the second PDN. 9.The method of claim 5, wherein the first information is received by aMobility Management Entity (MME), the second PDN, or an Evolved PacketSystem (EPS) bearer.
 10. The method of claim 5, wherein the firstinformation that the first PDN has failed is explicitly received.